KB5134123OOBOut-of-band release · 2026-10 OOB

Out-of-band release for Windows 10, version 1607 and Windows Server 2016

Support article Update Catalog CVEs in Security CVE list for a ticket

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It fixes actively exploited vulnerabilities. Deploy as soon as possible, and check the open known issues on your pilot devices first.

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Urgency Critical · 1 exploited Risk Moderate · 1 mitigated

Includes the security fixes of KB5126868
Fixes 1 exploited vulnerability; CISA deadline 16 Oct
Known issue (mitigated): Users might be unable to sign in to OWA or send emails on Exchange Server
Released 2 days ago
Some required public sources could not be fully read. The assessment may be missing issues or security fixes.

Everything in the October 2026 Patch Tuesday cycle

Companion updates for this Windows version

Same patch cycle

Windows and .NET Framework are serviced separately. These packages target the same Windows version; choose the framework packages that apply to your installation.

KB5127684.NET Framework

.NET Framework 4.8Win 10 1607 · Server 2016

13 Oct 2026

Companion updates do not replace this KB or establish an installation prerequisite.

2Windows versions

1Open known issues affecting it

MSRC lists no CVEs under this KB itself; it includes the security fixes of KB5126868 (769 CVEs).

Applies to

From Microsoft's release-information tables

Servicing branch	OS build	Release	Available
Windows 10, version 1607	14393.9615	OOB 2026-10 OOB	26 Oct 2026
Windows Server 2016	14393.9615	OOB 2026-10 OOB	26 Oct 2026

Known issues in this update

Includes issues from the update it builds on

Mitigatedfrom KB5126868Win 10 1607, Server 2016updated 16 Oct

Users might be unable to sign in to OWA or send emails on Exchange Server Issue reported on Exchange Server 2016, 2019, and Subscription Edition, affecting OWA sign-in and mail delivery.

Issues this update resolves

No resolved issues listed

Windows release health names no issues fixed by this KB in the collected data.

Page history

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Cite this version

Field-level log (2)

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28 Oct 2026 · 08:37:56 UTC Source coverage: windows-server-releasesCurrent → Incomplete
28 Oct 2026 · 08:37:56 UTC Source coverage: windows-10-releasesCurrent → Incomplete